1. Field of the Invention
The present invention relates to a seal device for effecting a gas seal in a rotating machine of a gas turbine and the like in which a high temperature gas flows.
2. Description of the Prior Art
FIG. 7 is a cross sectional view of a related portion of a prior art gas turbine. In FIG. 7, numeral 1 designates a turbine disc, which is fixed to a rotating shaft. Numeral 10 designates a moving blade, which is implanted in an outer circumferential portion of the turbine disc 1 and numeral 11 designates a stationary blade. A cooling air cavity 14 is formed between the turbine discs 1,1 of mutually adjacent stages and a labyrinth seal 15 is provided on an inner circumferential surface of the stationary blade 11 for effecting a gas seal between a gas path 12 and the cooling air cavity 14. Numeral 13 designates a cooling air passage for leading therethrough a cooling fluid into the cooling air cavity 14.
Numeral 2 designates a seal plate provided in the turbine discs 1, 1 on an inner side of the labyrinth seal 15. As shown in FIG. 8, the seal plate 2 is a thin metal ring, which is divided into plural pieces (two pieces in this example) in the circumferential direction. A divided part 2c has its upper and lower divided surfaces formed in stepped shapes, respectively, so as to be gas tight when they are mated with each other. The seal plate 2 is assembled into grooves 1a (see FIG. 2) provided in the mutually adjacent turbine discs 1, 1. While in operation, the seal plate 2 is pressed against outer circumferential wall surfaces 1b of the grooves 1a by the centrifugal force of the seal plate 2 itself due to a high speed rotation of the turbine discs 1,1, so that the cooling fluids is prevented from leaking into the gas path 12 side by a differential pressure between the gas path 12 and the cooling air cavity 14.
In the gas turbine using the mentioned prior art seal plate, the seal plate 2 is divided into plural pieces in the circumferential direction and so the fluid intrudes easily into the divided part 2c. Also, as the seal plate 2 is pressed against the outer circumferential wall surfaces 1b of the grooves 1a of the turbine discs 1,1 only by its own centrifugal force, the pressing force is small and self-induced vibration of the seal plate 2 is liable to occur when the fluid so intrudes. Thus, in the prior art seal structure as mentioned above, there is often caused abrasion or thinning of the seal plate 2 by the self-induced vibration, which results in the problem of deterioration of the sealing performance.